Tyrosine oxidation and protein turnover in maternal tissues and the fetus during pregnancy in rats.
Protein metabolism was examined in rats during the anabolic and subsequent catabolic phase of pregnancy. Protein synthesis in maternal muscle and liver, whole body amino acid flux and [14C]tyrosine oxidation was measured twice during each phase. Protein fractional synthesis and breakdown rates in the fetus and placenta were determined. 1. Muscle protein synthetic rate increased during the anabolic phase and fell during the catabolic phase. Muscle protein increased during the anabolic phase. 2. Liver protein increased by the end of pregnancy with no change in synthetic rates indicating reduced rates of breakdown. 3. Amino acid flux increased during the catabolic phase of pregnancy indicating increases in whole body protein synthesis. The increases were of sufficient magnitude to permit the deposition of protein occurring in fetuses and placentas during this period. 4. 14CO2 production from infused [14C]tyrosine remained unchanged during the anabolic phase of pregnancy but fell during the catabolic phase due mainly to dilution of label by increased amino acid flux. 5. Maternal protein anabolism is mediated by increased muscle protein synthesis rather than by decreased amino acid catabolism. 6. A 61% fall in protein breakdown rate assists fetal protein deposition during the last 4 days of pregnancy.
D000596:Amino Acids / Q000097:blood; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D010084:Oxidation-Reduction; D011247:Pregnancy; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014443:Tyrosine / Q000378:metabolism*
D000596:Amino Acids; D011506:Proteins; D002245:Carbon Dioxide; D014443:Tyrosine